Dinitrotoluene (DNT) is a versatile and valuable chemical intermediate which is widely used in the production of toluene diisocyanate.
DNT is produced by a process involving the nitration of toluene first to mononitrotoluene and then to DNT. Historically, the nitration reaction has been carried out commercially using a mixed acid system, namely, nitric acid and sulfuric acid. However, as a result of recent developments in this field, an alternative, improved process is now available for the commercial production of DNT which, among other things, obviates the need for using sulfuric acid in the nitration of toluene. See for example U.S. Pat. No. 5,001,272, issued Mar. 24, 1991 to Mason, and U.S. Pat. No. 5,009,078, issued Mar. 24, 1992 to Quakenbush, U.S. Pat. No. 5,302,763, issued Apr. 12, 1994 to Quakenbush, U.S. Pat. No. 5,354,924, issued Oct. 11, 1994 to Mason, and U.S. Pat. No. 5,488,187, issued Jan. 30, 1996 to Mason. All of these patents are incorporated herein by reference in their entirety.
The nitration reaction, whether using a mixed acid system or nitric acid by itself, typically results in the generation of undesirable byproducts, as well as a weight ratio of 2,4-DNT to 2,6-DNT isomers that may be higher or lower than desired. Illustrative undesirable impurities that typically result from the production of DNT include phenolic impurities, such as cresol compounds.
There is a continuing need in the DNT manufacturing community for a process, that advantageously can be operated continuously, and that provides a relatively fast reaction rate, a relatively low amount of impurities, and a DNT product having a desirable 2,4-DNT to 2,6-DNT isomer ratio. The present invention provides one answer to that need.